The invention relates to winding cores or winding cores, and relates in particular to cores or tubes for rolls of sheet metal.
Sheet metal such as steel, aluminum, and the like, is typically provided in bulk in the form of large rolls wound about cores. When winding rolls of heavier gauge metal, the stiffness of the wound sheet is usually high enough to withstand the weight of the roll, such that it is not essential to use a winding core, and quite often the metal industry uses “coreless” winding. However, when the metal sheet has been coated or oiled such that it is slippery, winding cores are usually necessary in order to be able to wind the rolls with sufficient tension from the very beginning of the winding process to compensate for the low coefficient of friction of the wound sheet. Only by winding with high tension can a self-supporting roll with good roll stability be achieved, and such high tension requires the use of a winding core. The winding core is typically a wound paperboard construction. The core is usually sleeved over a winding mandrel that is radially expandable to grip the core so that the core does not slip relative to the mandrel.
Additionally, winding cores are beneficial to prevent damage to the innermost layers of the sheet metal from forklift forks or lifting chains that are inserted into the rolls for moving them about. In an increasingly competitive and cost-conscious environment, end users want to be able to use the full length of the wound metal sheet, so that damage to the inner layers cannot be tolerated. Accordingly, winding cores are desirable even when not essential for good roll stability.
Because the core is only required for protection, customers want the core to be as inexpensive as possible. These fiber cores usually have a diameter of 16 inches, but other sizes are also commonly used. Shipping and storage of such large cores is very expensive and transport can be as much as 30 percent of total costs.